One day in 1987, in a small-to-medium-sized New England town, the normally restrained Frances Fitzgibbons, a 45-year-old widow, changes utterly. Suddenly conceiving a passion for the 18-year-old drum major who marches with the band every Saturday morning past her home, she successfully and ruthlessly seduces him (inviting him, during coitus, to insult his current girlfriend: "Say something worse!" "I will! I will!"; it is one of the most extraordinary sex scenes I have ever read, both ludicrous and arousing at the same time, which is quite a feat to pull off).

Next she goes to her job at the local bank and, taking full advantage of her suddenly awakened "gift for persuasive speech", manages, with equal ruthlessness and success, to become promoted with dizzying speed to the posts of senior vice president and chief executive officer, firing a few people along the way in order to instil a sense of terrified loyalty and devotion among the remaining staff.

Raymond Kennedy, who died in 2008, wrote this book in 1990 but set it during the financial crisis (a storm in a teacup compared to the current one) of October 1987, and indeed the scenes of anxious bank employees monitoring the collapse of the stock market have their resonances today.

Also, the sight of a sexually attractive woman in her 40s clawing her way to the top with a breathtaking mixture of sheer nerve, manic energy and a highly selective approach to veracity has prompted many people, including the book's blurb writer, to mention the name "Sarah Palin". (That Mrs Fitzgibbons also discovers a talent for gleeful profanity is also a nice touch.) In his other novels too, Kennedy seems to have had a fascination for scary, strong women with a penchant for seduction.

In Ride a Cockhorse, whose title appears less arbitrary the further one goes into the book, Mrs Fitzgibbons actually attempts to rape a man, and the scene is both horrific and comic – as one may indeed compare it with the sex scene with the drum major. For a while I thought that this book, obviously good though it is, had a major problem, in that it suggested that there is something nightmarish, or Against Nature, about a femmed'un certain age on the make, both sexually and professionally. But I think that if Kennedy is going to populate his novels with women who don't act like they oughter, then this means he finds the phenomenon not only almost obsessively fascinating but imaginatively rich. He's not being misogynistic.

Not least because there is, in fact, something deeply compelling about Mrs Fitzgibbons. She is, clearly, monstrous and manipulative, enjoying an almost sexual thrill when she fires people or makes them subservient to her will; but she sure as hell lights the story up (she is the story, of course) and we are, naturally, goggle-eyed to see what she'll get up to next.

Of those who fall under her spell – and there are many, as she dazzles the local print and TV news sources with her charisma and thought-free flow of high-octane entrepreneurial bullshit – it is said: "If anything, she may have represented to them a living symbol of the darker side of their mortal hopes."

I am always cautious of declaring something to be an allegory, and Kennedy, who knows how to create a fruitful ambivalence – the biggest one being that he makes it hard for us not to admire his antiheroine – presumably would not have declared this to be one. But there is no denying that it is so, in its very knowing demolition of the ideals of the sort of small-time savings and loan bank immortalised by Jimmy Stewart in It's a Wonderful Life. (It is impossible for a story to be set in such an institution without conjuring up comparisons.) "I'm going to overrun them!" she says of her competitors. "I'm not going around them, I'm going to roll over them."

The double entendres inherent in the rhetoric of predatory capitalism are well chosen, and the sooner we appreciate that it is all about us getting screwed, as well as a kind of exhilarating mania, the wiser we will be.